Evolution of the radio access scheme and the radio network for cellular mobile communication (hereinafter referred to as “Long Term Evolution (LTE)” or “Evolved Universal Terrestrial Radio Access (EUTRA)”) has been studied by the 3rd Generation Partnership Project (3GPP). According to LTE, as a communication scheme for radio communication from a base station device to a mobile station device (downlink), the Orthogonal Frequency Division Multiplexing (OFDM) scheme which is a multicarrier transmission scheme is used. As a communication scheme for radio communication from a mobile station device to the base station device (uplink), the SC-FDMA (Single-Carrier Frequency Division Multiple Access) scheme which is a single-carrier transmission scheme is used.
According to LTE, the base station device determines radio resource allocation, code rate, and modulation scheme for example, for a PUSCH (Physical Uplink Shared Channel) which is a channel for transmitting data by a mobile station device and a PDSCH (Physical Downlink Shared Channel) which is a channel for transmitting data by the base station device. The base station device also transmits downlink control information (DCI) indicating information such as the radio resource allocation to the mobile station device using a PDCCH (Physical Downlink Control Channel).
According to LTE, the mobile station device transmits uplink control information (UCI) such as acknowledgement indicating whether PDSCH has been successfully received or not (Acknowledgement or Non-Acknowledgement (which will be hereinafter referred to as “ACK or NACK” or “ACK/NACK”) and channel quality information (or also referred to as channel state information) indicating the quality of the downlink channel to the base station device using a PUCCH (Physical Uplink Control Channel). When the mobile station device transmits uplink control information, in the case where the PUSCH radio resource is allocated from the base station device, the mobile station device transmits the uplink control information not using the PUCCH but using the PUSCH.
The 3GPP has also studied a radio access scheme and a radio network that use a wider frequency band than LTE to implement still faster data communication (hereinafter referred to as “Long Term Evolution-Advanced (LTE-A)” or “Advanced Evolved Universal Terrestrial Radio Access (A-EUTRA)”). LTE-A requires backward compatibility with LTE, namely requires that a base station device of LTE-A should communicate by radio with both a mobile station device of LTE-A and a mobile station device of LTE simultaneously, and a mobile station device of LTE-A should be able to communicate by radio with both the base station device of LTE-A and the base station device of LTE. LTE-A has studied use of the same channel structure as that of LTE.
“Contention based uplink transmissions” (NPL 1) proposes to introduce contention based uplink transmission in order to improve the latency and the overhead in LTE-A. In contention based uplink transmission, a base station device transmits downlink control information that includes PUSCH radio resource allocation for example and can be received by a plurality of mobile station devices. A mobile station device detects the downlink control information and transmits the PUSCH based on the downlink control information. In the case of contention based uplink transmission, a plurality of mobile station devices may detect the same downlink control information. As a result, a plurality of mobile station devices use the same radio resource to transmit respective PUSCHs and thus respective PUSCHs from these mobile station devices are in contention (collide) with each other.
The contention based uplink transmission using the PUSCH is different from random access using a physical random access channel (Physical Random Access Channel: PRACH). The contention based uplink transmission and the random access are identical in terms of the possibility of contention (collision). They are different from each other in that a radio resource used for preamble transmission by the random access is the PRACH indicated by system information broadcasted by the base station device, while a radio resource used by the contention based uplink transmission is the PUSCH scheduled by the PDCCH.
For transmission of message 3 in the random access process, the PUSCH is used. After transmitting the preamble via the PRACH, the mobile station device transmits uplink data using a PUSCH radio resource scheduled by a random access response (message 2) while the possibility of collision still remains. In contrast, as for the contention based uplink transmission, preamble transmission via the PRACH is not performed, the base station device uses the PDCCH to schedule the PUSCH radio resource having the possibility of collision, and the mobile station device transmits uplink data using the scheduled PUSCH radio resource. Namely, the contention based uplink transmission does not involve the random access process.
According to LTE, basically access is made using a scheduling request (SR). The mobile station device uses a PUCCH or PRACH to request a PUSCH radio resource for transmitting uplink data. In contrast, regarding the contention based uplink transmission, the mobile station device does not make the scheduling request but can directly transmit uplink data, and therefore, the latency is improved as compared with the access method using the scheduling request. Unlike the PRACH, the PUSCH has no guard time. Therefore, only a mobile station device with valid uplink timing adjustment (Time Alignment) can access the base station device through contention based uplink transmission. The period for which the uplink timing adjustment is valid is a certain period (including infinity) from reception of uplink timing information (Timing Advance Command).